A ship's hull which is subjected to marine organisms is prone to barnacle growth and general fouling, making the hull surface rough and uneven. This leads to greater friction resistance when the ship is propelled through the water, which in turn means a significant increase in fuel consumption. It is known that a 1% increase in friction causes approximately a 3% fuel consumption increase. Frequent hull cleaning is therefore required, both from economical and environmental points of view.
Developing suitable and practical cleaning equipment for large surfaces, such as ships' hulls, is a considerable challenge, partly due to the hulls' limited accessibility when submerged in water.
Also, ships' hulls are commonly coated with toxic paints, containing organic tin compounds. Such compounds should not be dislodged from the hull, as they may contaminate the surrounding marine life. It is therefore desirable to use cleaning equipment that removes impurities (fouling, etc.) from the hull but damages the hull paint as little as possible.
The state of the art includes a number of devices for cleaning large surfaces, such as ships' hulls, comprising both the use of brushes and spraying with pressurized water through nozzles. Some devices have nozzles arranged on rotatable members, some have the nozzles arranged on an arm or on a ring-shaped member, while others have the nozzles arranged on a solid disc.
U.S. Pat. No. 4,926,775 discloses a cleaning device intended for use on mainly vertical surfaces under water. The apparatus comprises nozzles, arranged on a rotary disc, to spray water under high pressure against a surface. The rotational axis of the disc is mainly perpendicular to the surface to be cleaned. The nozzles are arranged obliquely, in order to provide the spraying water with a tangential motion component, leading to a reactive force that sets the disc in rotation. In addition one or more of the nozzles are directed away from the surface to be cleaned in order to maintain the apparatus in a position close to the same surface.
WO 2005/044657 discloses a device for cleaning under-water surfaces, such as ships' hulls. The device comprises a rotary disc having nozzles for discharging pressurized liquid against the surface to be cleaned. The nozzles are mounted obliquely in relation to the rotational axis of the rotary disc and are arranged to be supplied with pressurized liquid through a hollow spindle that is concentric with the rotational axis.
The state of the art also includes remotely operated vehicles (commonly referred to as an ROV) for carrying hull cleaning devices. One example is disclosed by KR 2008/0093536 A, describing an underwater robot for cleaning and inspecting a ship hull. The robot comprises wheels for rolling on the submerged hull, vertical/horizontal thrusters to induce movement in the vertical and horizontal directions, and a water jet spraying device. The robot wheels are driven by motor, whereby the robot is driven along the ship hull. The robot is remotely controlled from a console (above water), via an umbilical cable.
Another example of an ROV-carried hull cleaning device is disclosed by U.S. Pat. No. 4,462,328, describing a carriage with wheels for travelling along the ship hull and having a plurality of cleaning nozzles and a reactor nozzle aligned to produce a reactive force which opposed the force component of the cleaning nozzles which tends to urge the carriage away from the hull of a ship.
It is an object of this invention to provide cleaning device and vehicle which is more efficient and simpler to operate that those of the prior art.